Method of forming crack control slots

ABSTRACT

A method of forming and sealing crack control slots in concrete slabs including the major steps of forming a V-shaped crack control slot in the concrete when in the plastic state, dressing the groove using a carbide wheel having a V-shaped peripheral working edge, and sealing the groove using a backer cord and a plastic sealant. Preforming the slots in the V-shape tends to maintain the shape of the dressing wheel during the dressing operation for a substantially extended period.

United States Patent Peterson, Jr. et al. 1 Feb. 18, 1975 1 1 METHOD OF FORMING CRACK CONTROL 2.210.138 8/1940 Bishop 404/66 SLOTS 2.778.088 1/1957 Sterrett 264 162 2,915,110 12/1959 Ferguson 404/74 [75] Inventor Har y 8- t s Jr-, na 3,334,558 8/1967 Atkinson.. 52/396 Charles M. Peterson; Robert King, 3,416,415 12/1968 Worson 404/74 "I, both Of Franklin, all of Mich. 3,491,499 1/1970 Dyer 52/396 I 3,747,981 7/1973 Zuzelo 1 299/10 1 ASSlgfler-I Harry Peterson p y 1119-, 3,791,696 2/1974 Riley 299 10 Highland Park, Mich. [221 Filed; SQPL 25, 1972 Primary Examiner-Henry C. Sutherland Attorney, Agent, or Firm-Thomas N. Young [21] Appl. No.: 292,019

[57] ABSTRACT [52] US. Cl 52/744, 52/396, 299/10, A method of forming and sealing crack control slots in 404/74 concrete slabs including the major steps of forming a [51) Int. Cl. E0lc 11/06 V-shaped cr k control slot in the concrete when in [58] Field of Search 404/49, 74, 64, 66, 67; the plastic state, dressing the groove using a carbide 52/396, 743, 744, 749; 264/162, 184; 299/10 wheel having a V-shaped peripheral working edge, and sealing the groove using a backer cord and a plus [56] References Cited tic sealant. Preforming the slots in the V-shape tends UNITED STATES PATENTS to maintain the shape of the dressing wheel during the 1262.308 4/19", Colt n 264/162 dressmg operation for a substantlally extended perlod. 2,014,894 9/1935 Heltzel 404/74 4 Claims, 3 Drawing Figures )75 TROWEL 6533 SLOT co me SHAPED SHAPED 8p SLOT WHEEL LAY FILLER FILL SLOT 5f CORD WITH IN SLOT SEALANT PATENTEOFEB'B'STS 3,866,384

TROWEL DRESS SLDT POUR v- SHAPED YY 'JE CONCRETE SLOT 2f WHEEL LAY FILLER FILL SLOT 3{ SLOT I SEALANT 1 METHOD OF FORMING CRACK CONTROL SLOTS INTRODUCTION This invention relates to methods of forming and sealing crack control slots in concrete slabs and the like.

BACKGROUND OF THE INVENTION It is well known that concrete slabs in highways, parking structures, runways, and other environments have a tendency to crack due to thermal cycling and disturbances of the underlying bed or foundation. Accordingly, it is customary to form shallow slots in a regular pattern across the concrete slabs so that the cracks which ultimately do occur follow the slots and, thus, are straight and clean rather than jagged and irregular.

Studies which have been made of concrete and crack controls for concrete indicate that the crack control slots should have chamfered or rounded edges to avoid spalling and, moreover, should be sealed to prevent moisture and stone damage. In the past, the desired slot configuration has been accomplished by one of two alternative methods: the first involves sawing a slot in hardened concrete and then chamfering the upper edges of the slot witha wet grinding wheel; the second involves tooling in the slot while the concrete is in the plastic state. In either case, it is necessary to sandblast the slot clean to remove laitance and reformed cement washings thereby to obtain a surface to which a sealant will satisfactorily adhere.

The cutting and chamfering method has the disadvantage of wearing out both the cutting and chamfering wheels very rapidly, thus, requiring frequent wheel change or dressing. The tooling and cleaning method has the disadvantages of poor sealant adherence due to incomplete surface cleaning, the dust pollution and clean-up requirements inherent in a sandblasting operation, and extraordinary equipment and personnel requirements.

The sealing operation has also received attention in the prior art. One study concludes that the sealant slot should be straight-sided and that the sealant should be equal in depth to one half of the slot width. This slotsealant design performs poorly, however, in actual field tests due to spalling, as previously mentioned, and also due to the fact that traffic tends to drive the sealant down into the slot.

Sealants themselves have also been deficient in certain respects. The commonly used asphaltic type mastic tends to deteriorate with time, to lose adhesion to the concrete, and to accept stones and other imcompressible particles when soft.

BRIEF STATEMENT OF THE INVENTION In accordance with the present invention, the disadvantages of the prior art methods are substantially reduced or eliminated by way of a method of forming crack control slots of continuous and uniform configuration and in such a way as to substantially improve the performance of the finished slot and to facilitate the process of forming it. In general, this is accomplished by way of a two-step slot-forming process and a twostep slot-sealing process; the slot-forming process involving the steps of forming, such as by trowelling, a V- shaped slot into the concrete slab when in the plastic state and then cleaning or dressing the slot to remove laitance and other undesirable surface constituents using a cutting wheel of carbide or the like having a pcripheral working edge of substantially the same shape as that of the groove. Accordingly, the slot is cleaned to receive the sealant and the shape of the preformed groove tends to maintain the shape of the peripheral working edge of the dressing wheel, even though the wheel is gradually worn away during the cutting operation. Moreover, the configuration of the slot is inherently resistant to spalling and, thus, no separate chamfering step is required. The slot sealing steps are then carried out by installing a cord of inexpensive filler material, such as cellular polyethylene, into the slots and filling the upper portion of the slots with a suitable elastomeric sealant. The V-shaped slot inherently holds the sealantcombination in a compressive position under traffic loads.

The invention will be best understood by reference to the following specification which describes a specific embodiment of the invention in detail. This specification is to be taken with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of a concrete slab assembly having a crack control slot which is formed in accordance with the present invention;

FIG. 2 is a cross-sectional view of a concrete slab having a preformed slotof V-shape and a dressing wheel of corresponding peripheral configuration disposed in the slot; and,

FIG. 3 is a flow diagram of the essential steps involved in carrying out the present invention.

DETAILED DESCRIPTION OF THE SPECIFIC EMBODIMENT Referring first to FIG. 1, there is shown a concrete assembly comprising a topping layer 10 which is disposed over and bonded to a plurality of laterallyspaced, prestressed concrete tees of which tees l2 and 14 are representative. A crack control slot 16 is formed in the topping layer 10 in accordance with the present invention to provide a weakened area so as to locate in advance a later occurring vertical crack 18 in the space between the two laterally-spaced tees 12 and 14 and also to control the shape and appearance of the crack when viewed from the surface of the topping layer 10. It is to be understood that the specific application illustrated in the drawings is only one of many instances where the invention may be employed. Another very common application is the concrete highway or runway where a tee is placed in the concrete at the bottom of the slab and a control slot is formed directly over the tee.

In accordance with the present invention, the control slot 16 is of V-shape in cross section and is filled for sealing purposes with a foamed polyethylene filler cord 20 and a polyurethane sealant 22 which remains reasonably flexible over a broad temperature range and which achieves a permanent adherence to concrete. Assuming the topping layer 10 is approximately two and one-half inches thick, the control slot 16 is approximately one inch deep and one-half inch wide at the top surface of the topping layer 10. The foamed polyethylene cord 20 is typically one-quarter to three-eights inch in diameter and is installed under compression.

The representation of FIG. I is a typical embodiment or result of the present invention and is formed by the steps which are represented diagrammatically in FIG.

3 3, of which the dressing step is graphically illustrated in FIG. 2.

Looking to FIG. 3, the steps of the present invention are shown to comprise a step 24 of pouring the concrete topping layer over the foundation which in this case comprises the plurality of prestressed concrete tees l2 and 14. Following the pouring of the topping layerl0 in accordance with step 24 and while the concrete is still in a plastic state, the step 26 is carried out by trowelling or otherwise forming the V-shaped slot l6 into the topping layer 10. Again, the width and depth of the slot 16 are preferably one-half inch and one inch, respectively, and is formed by means of a grooving tool having av-shaped working edge. After the concrete with the preformed but undressed V- shaped slot 16 is formed in accordance with steps 24 and 26, step 18 is carried out by dressing or cleaning the slot 16 using a carbide dressing wheel 30, as shown in FIG. 2, having a V-shaped, peripheral edge of substantially the same dimentional configuration as the preformed slot 16 in the topping layer 10. The configuration of the wheel 30 is preferably such as to slightly overhang the edges of the preformed slot 16, as shown in FIG. 2, so as to round off those edges and reduce the tendency for cracking or spalling along the edges at some future time. The dressing wheel 30 tends to wear in such a fashion as to be reduced in radial dimension during the cutting operation but, because of the V- shape of the preformed slot 16, the dressing wheel 30 tends to maintain its working edge configuration thereby saving the operator the time and expense of frequent dressing wheel changes and/or sharpening operations. Moreover, the result is a cleanly dressed slot 16 of uniform and continuous configuration and dimension.

At the completion of step 28 the slot 16 is fully formed and ready for sealing. The sealing of the slot 16 is carried out first by step 32 which involves placing the one-quarter inch polyethylene rope 20 into the slot under compression to act as a filler or backer material. The one-quarter inch cord 20 leaves approximately one-half to three-eights inch of depth to be filled with sealant in accordance with step 34. The sealant 22 is then poured into the upper portion of-the slot 16 and is topped off substantially flush with or slightly below the upper surface of the topping layer 10 and allowed to cure. When finished, the sealant strip is trapezoidal in cross-section and is positionally stable under traffic compression due to the taper of the slot 16. This can be readily contrasted to the straight-sided slot with the sealant formed at the top in a rectangular cross-section where traffic loads tend to place the sealant in tension. thus, to promote failure.

It is to be understood that various additional steps and modifications of the existing steps may be made in accordance with the particular application of the crack control slot forming method disclosed herein.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

l. A method of producing a concrete topping structure disposed over a foundation and having at least one sealed crack control slot formed therein and comprising the steps of:

a. Casting a topping layer of concrete over a suitable foundation;

b. Forming by tooling a Vshaped slot in and across the exposed surface of the topping layer while the concrete of said layer is in the unset plastic state;,

c. Permitting the topping layer to substantially cure with the V-shaped slot formed therein;

d. Dressing the walls of the slot with a rotary abrading apparatus which conforms to the configuration of I the slot to remove laitance and weak concrete from the slot while preserving the tooled configuration thereof, and

e. Thereafter sealing the slot by filling at least a portion of the slot with a curable flexible polymeric sealant material which, when cured, remains flexible and which adheres to the dressed concrete walls of the slot.

2. The method defined in claim 1 wherein the rotary apparatus comprises a dressing wheel having a compound beveled peripheral edge which substantially conforms to the tooled configuration of the slot such that the peripheral bevels of the dressing wheel are in full facial contract with the walls of the slot during the dressing operation.

4. The method defined in claim 7 wherein the foundation comprises at least two precast concrete members defining a joint therebetween, the slot being formed directly over and in substantial alignment with said joint. 

1. A METHOD OF PRODUCING A CONCRETE TOPPING STRUCTURE DISPOSED OVER A FOUNDATION AND HAVING AT LEAST ONE SEALED CRACK CONTROL SLOT FORMED THEREIN AND COMPRISING THE STEPS OF: A. CASTING A TOPPING LAYER OF CONCRETE OVER A SUITABLE FONDATION; B. FORMING BY TOOLING A V-SHAPED SLOT IN AND ACROSS THE EXPOSED SURFACE OF THE TOPPING LAYER WHICH THE CONCRETE OF SAID LAYER IS IN THE UNSET PLASTIC STATE; C. PERMITTING THE TOPPING LAYER TO SUBSTANTIALLY CURE WITH THE V-SHAPED SLOT FORMED THEREIN; D. DRESSING THE WALLS OF THE SLOT WITH A ROTARY ABRADING APPARATUS WHICH CONFORMS TO THE CONFIGURATION OF THE SLOT TO REMOVE LAITANCE AND WEAK CONCRETE FROM THE SLOT WHILE PRESERVING THE TOOLED CONFIGURATION THEREOF, AND E. THEREAFTER SEALING THE SLOT BY FILLING AT LEAST A PORTION OF THE SLOT WITH A CURABLE FLEXIBLE POLYMERIC SEALANT MATERIAL WHICH, WHEN CURED, REMAINS FLEXIBLE AND WHICH ADHERES TO THE DRESSED CONCRETE WALLS OF THE SLOT.
 2. The method defined in claim 1 wherein the rotary apparatus comprises a dressing wheel haviNg a compound beveled peripheral edge which substantially conforms to the tooled configuration of the slot such that the peripheral bevels of the dressing wheel are in full facial contract with the walls of the slot during the dressing operation.
 3. The method defined in claim 1 wherein the step of sealing the slot comprises the additional step of placing a filler cord in the dressed and cured slot prior to filling the slot with the curable flexible polymeric sealant whereby the sealant, when cured, is substantially flush with the exposed surface of the topping layer.
 4. The method defined in claim 7 wherein the foundation comprises at least two precast concrete members defining a joint therebetween, the slot being formed directly over and in substantial alignment with said joint. 